The present invention is generally directed to a test system and, more specifically, to an indentation hardness test system.
Hardness testing has been found to be useful for material evaluation and quality control of manufacturing processes and research and development endeavors. The hardness of an object, although empirical in nature, can be correlated to tensile strength for many metals and provides an indicator of wear-resistance and ductility of a material. A typical indentation hardness tester utilizes a calibrated machine to force a diamond indenter (of a desired geometry) into the surface of a material being evaluated. The indentation dimension (dimensions) is (are) then measured with a light microscope after load removal. A determination of the hardness of the material under test may then be obtained by dividing the force applied to the indenter by the projected area of the permanent impression made by the indenter.
In a typical situation, an operator of an indentation hardness tester is required to position indents into a part at precise distances from various part geometries. With reference to FIGS. 2 and 3, an operator may be required to place a series of five evenly spaced indents 302 into a surface of a tooth 102A of a portion of, for example, a gear 102 being tested and mounted within a plastic 104 to form a test assembly 22. The indents 302 may be spaced 200 microns (±5 microns) from each other and centered in a face of the tooth 102A. Assuming that the tooth 102A is approximately 0.5 cm wide by 0.5 cm tall and the tester has two magnifications, i.e., a high power 50× objective with a field of view 200 microns wide and a 5× magnification with a field of view 2000 microns wide, and assuming that an image of the tooth 102A is displayed on a display having a width of 640 pixels, the width of each pixel is about 0.3 microns at 50× and about 3.0 microns at 5× magnification.
In such a tester, a 5× magnification only allows an operator to see about ⅕th of the top surface of a tooth and a 50× magnification only allows the operator to see about 1/50th of the top surface of a tooth. It should be appreciated that such a view does not allow an operator to precisely know if a stage that is used to position the test assembly 22 is positioned in the center of the top surface of the tooth. Thus, to ensure that indentations are perpendicular to the top of the tooth 102A and a specified distance from the top surface of the tooth 102A, traditional software packages have allowed an operator to position a “T” bar along a displayed image. In this manner, an operator would position the top portion of the “T” bar along the top edge of the tooth 102A through a combination of moving the stage and rotating the “T” bar. As briefly described above, at 5× magnification the operator has a relatively good idea of the required orientation of the “T” bar, but not enough resolution to position it within 5 microns of the edge. Further, at 50× magnification, locating the top edge of the tooth within 5 microns is possible, but the orientation is difficult because the edge is not straight at this magnification.
What is needed is a technique that more readily allows an operator of an indentation hardness tester to properly position an indenter with respect to a test assembly.